This project is an extension of previous work directed toward the study of noninvasive methods to determine spatial and temporal relationships existinng between tissues of clinical interest. The approach involves in vitro modelling of promising systems and the development of prototypes suitable for clinical evaluation. Recent work has focused on studies directed toward development of a versatile computerized radiographic system designed to be used both fluoroscopically and off-line to produce images which can be subtracted to show small changes in tissue occurring over long intervals of time, and combined in ways permitting tomographic display of specific slices of individual teeth. An all-electronic prototype has been fabricated which couples a specially developed intraoral x-ray source having a 10 focal spot which can be positioned electronically in a circular locus on an extended target, to a video-based fluoroscopic image-intensifier system. Preliminary tests with a cadaver specimen show that clinically meaningful subtraction images result from selection of appropriate projections taken on two different occasions without the need for an occlusal stint to stabilize projection geometry. Other tests confirm earlier computer simulations which demonstrated the ability to reconstruct any desired tomosynthetic slice from the same eight circularly distributed radiographic projections exhibiting a total angular disparity of only eight degrees. Other work has centered on the analysis of variations in x-ray projections produced by small changes in projection geometry. A rigorous model has been developed and tested which enables the application of statistical theory to determine the detectibility of specified lesions by ideal systems in the presence of empirically determined changes common to conventional radiographic practices. Related work also demonstrated that some of the observed variance attributable to small changes in projection geometry can be eliminated retrospectively by means of suitable affine and quadratic transformations.